Utilization of Probiotics to Manage Epizootic Shell Disease in American Lobsters, Homarus americanus

Melissa Hoffman

doi:10.23860/thesis-hoffman-melissa-2018

Abstract

Epizootic shell disease (ESD) in the American lobster, Homarus americanus, has a major impact on the southern New England lobster industry, yet there are no practical tools for managing the disease. The goal of this study was to identify bacterial probiotics that could be used to manage ESD in wild lobster populations. Candidate bacterial isolates (n = 24) were previously isolated from lobsters in Narragansett Bay and identified as having probiotic characteristics against ESD-associated bacteria Thalassobius sp. and Aquimarina macrocephali, or the fish pathogen Vibrio anguillarum. Healthy lobster post-larvae were exposed to five of the candidate strains isolated from lobsters and a probiotic bacterial strain isolated from the Eastern oyster, Crassostrea virginica (Phaeobacter inhibens S4). After several weeks of treatment, there were no significant differences in molting frequency, mortality, or growth of treated lobsters when compared with the control, indicating the candidate probiotics do not adversely affect lobster post-larvae. The effect of selected candidate probiotics (n = 3) on progression of ESD in adult lobsters was tested for three months. Frequent molting due to high disease severity confounded long-term effects of the treatments, and no significant differences were seen in mortality, molting, growth, or disease progression. These results highlight the challenges involved in the development of tools for the management of a chronic disease with a poorly understood etiology. Future research should focus on a better understanding of microbe-microbe-host interactions in ESD, and the effect of environmental conditions on these interactions.

Highlights

Heavy economic and cultural dependence on American lobsters (Homarus americanus) make coastal communities and stakeholders vulnerable in the face of disease outbreak
Healthy lobster post-larvae were exposed to five of the candidate strains isolated from lobsters and a probiotic bacterial strain isolated from the Eastern oyster, Crassostrea virginica (Phaeobacter inhibens S4)
While probiotic screenings have been conducted in other juvenile crustacean species for disease control applications, such as the spiny lobster, Panulirus ornatus, (Nguyen et al 2014), crayfish (Safari and Paolucci 2017), and various shrimp species (Hai and Fotedar 2010; Kumar et al 2016), these experiments have never been conducted for Homarus americanus in the context of Epizootic shell disease (ESD)

Summary

Introduction

Heavy economic and cultural dependence on American lobsters (Homarus americanus) make coastal communities and stakeholders vulnerable in the face of disease outbreak. In 1996, ESD was reported in lobsters in Rhode Island (Castro and Angell 2000). Since this onset, annual lobster catches in Rhode Island have reduced significantly, with annual landings falling in value from $19 million in the 1990’s to around $12 million in 2015 (NMFS 2016). Annual lobster catches in Rhode Island have reduced significantly, with annual landings falling in value from $19 million in the 1990’s to around $12 million in 2015 (NMFS 2016) It was estimated in 2012 that 10-30% of lobsters in Rhode Island had ESD (Castro and Somers 2012). This proportion of disease prevalence was even higher in egg-bearing female lobsters, where prevalence was reported at 60-80% (Castro and Somers 2012). While ESD prevalence remains low in the Gulf of Maine, the mean prevalence has more than doubled in the past 8 years from 0.5% to 1.2% (Reardon et al in press)

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